The Investigation On Planar And Channel Waveguides Fabricated By Ion Implantation And Ion Exchange

Waveguide is a basic structure in optical devices and plays an important rule in the fabrication of various optical devices because of its excellent characteristics, possibility in integration and rather low cost in manufacturing.It can confine the optical energy in small space and improve the optical energy density.The specific properties of the waveguide have made it play an important role in the fabrication of various optical devices.There are several conventional techniques for fabricating optical waveguides,including metal diffusion,epitaxial grouth,ion exchange and ion implantation.In the present work,ion exchange and ion implantation have been exploited for fabricating optical waveguides,and their performances have been studied.In all the implanted waveguides,MeV H and He ions are most frequently used, which build up an optical barrier at the end of the track due to the damage induced by nuclear energy loss.Such an optical barrier confines the light in an "optical well" between itself and the surface.However,one of the difficulties is that light ion implantation for the waveguide formation often needs much high doses of～10¹⁶ ions/cm².The dose of heavy ion implantation can be 1～3 order lower than that of light ion implantation and it can reduce the fabrication cost significantly.Therefore,the investigation on heavy ion-implanted waveguide is important not only for the theoretical study but also for the potential application as well.Ion exchange is that the doping ions exchange with the special ions of the substrate,which causes the changes of the refractive index in the substrate;as a result, the optical waveguide structure is formed.Most optoelectronics devices such as optical coupler,modulator,optical switch and waveguide laser are based on channel waveguide structure.The attempt of fabrication of such waveguide structure is necessary for both optoelectronics technology itself and the combination between nuclear technology and optoelectronics.1.53μm is the centric wavelength of third telecommunication window since standard silica-based optical fibers have their maximum transparency at this wavelength.The transition from the first excited state to the ground state in Er³⁺just occurs at this wavelength(1.53μm).And trivalent erbium(the preferred bonding state) has an incomplete 4f electronic shell that is shielded from the outer world by closed 5s and 5p shells.As a result,rather sharp optical intra-4ftransitions can be achieved from erbium doped materials.Several ways and hosts are currently under investigation for doping the host crystal with Er³⁺,with the aim to control erbium distribution and concentration in the host crystal,as well as its site location.The work we have done in this dissertation is focused on three aspects:(1)The waveguides fabrication by ion implantation technique:We have studied the waveguides formation in KTiOPO4 and RbTiOPO4 crystals by MeV heavier ion implantation,and analyzed the modes of the waveguides,measured the propagation loss,studied the annealing behavior of these waveguides.Since the ion implantation is a universal technique for the waveguide fabrication,therefore it is of particularly efficiencies for the new waveguide formation and characterization.The waveguides in KTa_1-xNb_xO₃,Nd:CNGG and Yb:GdVO₄ crystals have been fabricated by ion implantation.(2)The planar and channel KTiOPO₄ waveguides fabricated by combining ion implantation and ion exchange techniques:The double waveguides in KTiOPO₄ crystal have been formed by combining ion exchange and ion implantation. The mono-mode low loss KTiOPO₄ waveguide has been formed by ion implantation and then ion exchange.By making the mask with photoresist using lithography,the channel KTiOPO₄ waveguide was fabricated by combining ion exchange and ion implantation.(3)The investigation of doping ways and the crystal hosts of Er³⁺ions: we have exploited ion exchange process on doping KTiOPO₄ and KTiOAsO₄ crystals with Er³⁺ions.Moreover,we have utilized Er³⁺implantation into KTiOPO₄ and KTiOAsO₄ crystals.The RBS technique was used to analyze these doped samples. The details and results in this dissertation are listed as follows:KTiOPO₄(KTP)is an important nonlinear optical crystal with relatively larger nonlinear optical and electrooptic properties.It has found applications in Q-switching, second harmonic generation(SHG),optical parametric oscillation(OPO),and a variety of optical wave mixing application.To our knowledge,it is the first time to report the monomode enhanced-index KTP waveguide.The propagation loss of the waveguide,which was measured with the moving fiber method,can be reduced to less than 1.0 dB/cm after moderate annealing.We have analyzed the reasons that cause the refractive index change in KTP waveguide.The channel waveguide was fabricated in KTP crystal by using the photolithography process and then 6.0 MeV C ion implantation at dose of 5×10¹³ions/cm².Rubidium titanyl phosphate,RbTiOPO₄(RTP)is an orthorhombic crystal, isostructural with the well known potassium titanyl phosphate,KTP,non-linear optical crystal.RTP has high non-linear optical and electrooptical coefficients that could drive to important applications in non-linear optics and electrooptics.In this work,we have formed the planar waveguides in RTP crystal by MeV C ion implantation with low dose.The monomode enhanced-index RTP waveguide were first formed after moderate annealing.The dependences of refractive indices changes and mode plots versus implanted doses were analyzed.Annealing treatment was performed.The behavior of annealing on guiding mode and propagation loss were studied.Potassium tantalate niobate(KTa_1-xNb_xO₃,KTN)is a solid solution of KTaO₃ and KNbO₃,which has nearly the same unit cell size in their cubic phase.KTN is a promising material for optical devices because of its large electro-optic efficient. Electro-optic switches and modulators with optical waveguide are important devices for realizing faster digital communication applications.The structural uniformity of cubic KTN might also overcome the polarization dependence.Planar optical waveguides in KTN crystals were formed by 3.0 MeV C ions and 500 keV protons implantation with different doses,respectively.Reflectivity calculation method(RCM) was applied to simulate the refractive index profile in waveguides.The SRIM'2006 (The Stopping and Range of Ions in Matter)code was applied for simulating the process of the ion implantation in order to obtain a better understanding for the waveguide formation.Neodymium-doped calcium niobium gallium garnet(Nd:CNGG)is an attractive laser material suitable for diode pumping belong to the class of neodymium-doped disordered crystals.It has a relatively broader pump absorption band than Nd:YAG. Due to its large emission bandwidth originated from the disordered nature of the crystal,Nd:CNGG is a suitable candidate for diode pumped tunable mode locked lasers.Laser crystals doped with Yb³⁺have attracted considerable attention in the past decade.The gadolinium vanadate(GdVO₄)single crystal is an excellent laser host material with good laser properties,mechanical properties and chemical stability.In the present work,we firstly report on the fabrication of planar waveguides in Nd:CNGG and Yb:GdVO₄ crystals by 6.0 MeV C³⁺ion implantation at room temperature. Combined application of ion implantation and ion exchange treatment has been reported.Kostritskii et al.fabricated photorefractive waveguides(PRWs)by He⁺ implantation in LiNbO₃ doped via proton-assisted copper exchange.Opfermann et al. demonstrated the formation of buried optical channel waveguides by He⁺ implantation into Rb-exchanged KTP.Schrempel et al.found that rapid thermal annealing up to temperatures of 500℃was suitable to abolish point defects and to prevent the Rb-diffusion at the same time.We have recently formed the double waveguide by ion implantation into ion-exchanged KTP crystal and studied comprehensively the properties of the double waveguide.Monomode low loss KTP waveguides have been formed by ion implantation with 500 keV O⁺ ions at a dose of 1×10¹⁵ions cm^-2and the following ion exchange in pure RbNO₃ at 340℃for 45 min.Optical channel waveguide in KTiOPO₄ crystal has been fabricated by combining ion exchange with ion implantation.We doped Er ions into KTiOPO₄ and KTiOAsO₄ crystals by ion implantation technique.The depth profiles of erbium ions in the hosts are analyzed by RBS technique.There are two peaks of Er distribution in KTiOPO₄ after annealing.Some of Er has migrated toward the surface of the crystal.The remained Er was trapped at damage region.We have firstly exploited ion exchange process for doping KTiOPO₄ and KTiOAsO₄ crystals with Er ions.RBS technique is used to analyze the doped samples and gives the Er concentration values at the surface of each sample,and the concentration values is up to 3.5×10²⁰ions/cm³.